US20100068566A1 - Method for minimizing membrane electrode degradation in a fuel cell power plant - Google Patents

Method for minimizing membrane electrode degradation in a fuel cell power plant Download PDF

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Publication number
US20100068566A1
US20100068566A1 US12/448,124 US44812409A US2010068566A1 US 20100068566 A1 US20100068566 A1 US 20100068566A1 US 44812409 A US44812409 A US 44812409A US 2010068566 A1 US2010068566 A1 US 2010068566A1
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Prior art keywords
fuel cell
electrical load
cell stack
air
membrane
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US12/448,124
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English (en)
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Sathya Motupally
Carl A. Reiser
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04544—Voltage
    • H01M8/04559—Voltage of fuel cell stacks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04604—Power, energy, capacity or load
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H01M8/04753—Pressure; Flow of fuel cell reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04858—Electric variables
    • H01M8/04925—Power, energy, capacity or load
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • This invention relates to fuel cell power plants, and more particularly to power plants having PEM fuel cells. Still more particularly, the invention relates to the avoidance or minimization of degradation of the membrane of such fuel cells.
  • the polymer electrolyte/proton exchange membranes (PEM) in fuel cell stacks of fuel cell power plants are subject to degradation as the result of peroxide formation and/or existence in the vicinity of the membrane.
  • This peroxide can dissociate into highly reactive free radicals, which can in turn degrade the membrane. This interferes with the desire to achieve 40,000-70,000 hour and 5,000-10,000 hour lifetimes for stationary and transportation PEM fuel cells, respectively.
  • plane of potential change This plane of potential change is conveniently designated “X o ”, and represents where the reaction potential abruptly shifts from a low value to a high value.
  • X o represents where the reaction potential abruptly shifts from a low value to a high value.
  • the location of X o depends largely on the oxidant and fuel gas concentrations at locations on either side of that plane of potential change.
  • a protective “underlayer” of ionomer material containing a particulate catalyst has been provided between the membrane and the cathode.
  • the protective underlayer serves to scavenge oxygen and hydrogen during normal operation and thus forces X o to reside within the protective layer.
  • an air-starvation protocol serves to keep X o within the protective underlayer.
  • the use of the protective underlayer is viewed as effective in mitigating the problems described, it nevertheless represents the inclusion of an additional structure in the MEA. More specifically, the use of the protective underlayer both adds to the cost of the MEA as well as having some adverse impact on the performance of the MEA by causing an increase in ionic resistance between the electrodes.
  • catalyst e.g. Pt
  • dissolution takes place during excursions to high voltage that occur during idle or off-load conditions.
  • the catalyst typically deposits at the X o plane, and it is important to keep X o out of the membrane during these conditions. This is accomplished by voltage clipping, air starvation, or a combination of both, without requiring a protective underlayer.
  • a fuel cell power plant comprises a fuel cell stack including a plurality of membrane electrode assemblies, each having a cathode with a catalyst and a reactant air flow field and an anode with a reactant fuel flow field on opposite sides of a proton exchange membrane, the cathode catalyst having an interface with the membrane; an air supply connected to the air flow fields for providing reactant air to the cathodes; a fuel supply connected to the fuel flow fields for providing reactant fuel to the anodes; and a primary electrical load selectively powered by said fuel cell stack; and the invention is characterized by a plane of potential change normally occurring outside the proton exchange membrane at or near the cathode catalyst/membrane interface during operation of the fuel cell stack for electrical load cycling of the primary electrical load, but inside the proton exchange membrane during periods of relatively idle operation; at least one of: an interrupter operatively connected with the air supply and the cathode air flow fields for selectively interrupting the supply of air to the flow fields and a secondary electrical load for selective connection
  • both the air supply interrupter and the secondary electrical load are present, and the controller acts to control both to maintain the plane of potential change outside the proton exchange membrane also during periods of relatively idle operation.
  • the extent to which each of the air supply interrupter and the secondary electrical load are controlled may be a function of their respective efficiency penalties in the fuel cell power plant.
  • a method for mitigating decay of a membrane electrode assembly in a fuel cell comprises selectively operating a membrane electrode assembly in an electrical load cycle and in relatively idle operation, the membrane electrode assembly having a cathode with a catalyst and a reactant air flow field and an anode with a reactant fuel flow field on opposite sides of a proton exchange membrane, the cathode catalyst having an interface with the membrane, and operating the membrane electrode assembly differently between an electrical load cycle and a period of relatively idle operation for maintaining a plane of potential change between the anode and the cathode to be outside the proton exchange membrane and in the cathode throughout operation in both an electrical load cycle and a period of relatively idle operation.
  • the method is conveniently effected by controlling one, or both, of the electrical loading on the fuel cell and the supply of air to the cathode, as a function of electrical demand on the fuel cell.
  • the extent to which each of the electrical loading on the fuel cell and the supply of air to the cathode is controlled may be a function of their respective efficiency penalties.
  • the monitored electrical demand to effect control action may be any combination of power or current or output voltage from the fuel cell to the primary electrical load, with an individual cell voltage of about 0.85 to 0.9 volts serving as one prominent threshold parameter.
  • the FIGURE is a schematic illustration of a fuel cell power plant having a fuel cell membrane electrode assembly and associated load and controls, functionally illustrating the arrangement for maintaining the X o plane outside the membrane under load/no load conditions in accordance with the invention.
  • a fuel cell power plant 10 including a fuel cell stack 12 comprising a plurality of contiguous membrane electrode assemblies (MEA), each having a proton exchange (or polymer electrolyte) membrane (PEM) 14 between an anode 16 and a cathode 18 on opposite sides thereof, only one membrane electrode assembly 20 being shown in the Figure.
  • MEA contiguous membrane electrode assemblies
  • PEM proton exchange membrane
  • the electrical output at the positive and negative terminals of the fuel cell stack 12 is connected by a pair of lines 22 , 24 through a switch 26 to a normal, or primary, electrical load 28 .
  • the normal load 28 may be an electric motor associated with an electric propulsion system for a vehicle or it may be any of a variety of other known electrical loads that are operated/powered by the fuel cell stack 12 during normal operation.
  • the anode 16 includes a gas diffusion layer 30 for the introduction of hydrogen (H 2 ) from a source (not shown in detail) via line 32 to the anode 16 .
  • a gas diffusion layer 34 associated with the cathode 18 serves to admit oxidant reactant, such as air from air supply blower 36 , to the cathode 18 via line 38 .
  • the membrane electrode assembly 20 is operated by feeding oxygen through the gas diffusion layer 34 to cathode 18 and by feeding H 2 through gas diffusion layer 30 to anode 16 . These reactants support generation of an ionic current across the membrane 14 as desired.
  • the fuel cell power plant 10 and membrane electrode assembly 20 may also include a water circulation system/water transport plates (not separately shown here). Similarly, other aspects of a conventional fuel cell power plant not essential to an understanding of the invention are omitted from the Figure and description for the sake of brevity, but their presence is assumed.
  • Both the anode 16 and the cathode 18 are porous layers containing suitable respective catalysts.
  • the respective catalysts are at the surfaces of the anode and cathode that are in contact with the membrane electrode assembly 20 .
  • those catalysts may even be adhered to the surfaces of the membrane electrode assembly 20 , but in each event form a respective interface between the membrane and the respective cathode catalyst or anode catalyst.
  • catalyst materials which are typically present in the anode and cathode electrodes can dissolve and then precipitate elsewhere in the assembly.
  • the Figure depicts a broken line V in the membrane electrode assembly 20 which is illustrative of the relative electrical potential at that location in the assembly.
  • V the membrane electrode assembly 20
  • X o the relative electrical potential change between the electrodes, where the potential abruptly shifts from a low value to a high value.
  • the position of X o depends heavily on the oxidant and reductant gas concentrations at locations on either side off X o .
  • dissolved catalyst tends to precipitate at X o and further, that the electrically isolated catalyst particles can increase the formation of peroxide and/or radicals. Because of the potentially degrading characteristics of such activity on the membrane 14 if it occurs within the membrane, it is important to avoid such activity at that location.
  • the power plant 10 is configured and operated such that the fuel cell stack 12 , and thus the membrane electrode assembly 20 , are operated in a manner to assure that the X o plane of abrupt potential change is in, and remains in, an X o operating region 40 that is outside the membrane 14 and within the cathode 18 , whether in normal on-load operating conditions (i. e. electrical load cycling) or in off-load (i. e., relatively idle) conditions. While such positioning of the X o plane may not entirely prevent some of the adverse activity attendant to its presence, such as peroxide formation, it nevertheless removes it from the more-sensitive membrane 14 to the relatively less-sensitive cathode 18 .
  • the electrical load on the stack 12 is sufficient, though perhaps varying, to assure that the consumption of H 2 and oxygen occurs at a rate that places their interface, and thus the X o plane, clearly outside the membrane 14 and within the X o operating region 40 .
  • the electrical potential between the electrodes, and thus lines 22 and 24 is less than 0.9 V, typically being in the range of 0.55 to 0.85 volts.
  • the power plant 10 additionally includes at least one, and typically two, controlled arrangements for maintaining the X o plane outside the membrane 14 and within the desired X o operating region 40 within the cathode 18 .
  • either one or both, of the electrical loading on the fuel cell stack 12 and the supply of air to the cathode 18 are controlled as a function of the electrical demand on the fuel cell stack 10 . That electrical demand may be monitored and/or determined typically as a measure of voltage, current and/or power, though cell stack temperature may also be relied upon as an indirect indicator.
  • One end terminal of the fuel cell stack 12 provides the reference voltage that appears on the line 22 , and is additionally extended to a controller 50 and also to a secondary, or auxiliary, load 52 .
  • the secondary load 52 has for purposes of simplicity of illustration been shown in the Figure as a variable resistance, but it will be understood that it might alternatively or additionally be a battery, a capacitor and/or some other energy storage device.
  • the type of device selected as secondary load 52 may be determined by the degree to which it does/does not impose an efficiency penalty on the fuel cell power plant. For example, an energy storage device such as a capacitor might be favored relative to a pure power-dissipating resistance.
  • the other end terminal of the fuel cell stack 12 provides the potential difference that is developed across the fuel cell stack under a respective connected load, and appears on line 24 .
  • Line 24 provides an input to the controller 50 , and as noted previously, is connected to a terminal of switch 26 .
  • Switch 26 is functionally illustrated as being of the single-pole, double-throw type, and is operable to connect line 24 to either line 24 ′ connected to the primary load 28 or to line 24 ′′ connected to the secondary load 52 .
  • a current detector 54 connected to the controller 50 and operatively associated with line 24 or 22 provides a measure of the current to the controller.
  • the voltage across lines 22 and 24 is also provided as an input to the controller 50 .
  • Additional measures of the electrical loading of the fuel cell stack 12 by the electrical load, as for instance stack temperature, may also be supplied to controller 50 .
  • the controller 50 uses one or more of these inputs to measure electrical demand by the connected load on the fuel cell stack to thereby determine transitions between a normal cyclical load regime and an idle or no-load regime. This is perhaps most conveniently achieved by monitoring the potential between lines 22 and 24 , since it is preferable to keep such potential below about 0.85 volts in the no-load condition to maintain the X o plane within the desired X o operating region 40 .
  • a control line 56 connected from controller 50 to switch 26 serves to toggle that switch such that a/the secondary load 52 is connected between lines 22 and 24 .
  • the secondary load 52 may replace the primary load 28 across the lines 22 and 24 , as by the illustrated switching arrangement, or it may simply be connected in parallel with that primary load 28 during such time as that primary load is operating to impose little or no load on the stack.
  • the inclusion of the secondary load 52 may serve to assure that the potential between lines 22 and 24 is maintained below about 0.9 V, i.e., “clipped”. It will be appreciated that the impedance/resistance of the secondary load 52 may be controllably varied by control line 58 from controller 50 if such is deemed desirable as part of the control scheme.
  • the location of the X o plane may also be maintained within the desired X o operating region 40 during no-load or idle operation by interrupting,. or restricting (“starving”), the amount of air that is supplied to the cathode 18 .
  • This has the effect of relatively moving the X o plane away from the membrane 14 to remain in the cathode 18 .
  • the air from air supply blower 36 is connected to a two-way diverter valve 60 , one output of which is connected to cathode 38 via line 38 and gas diffusion layer 34 , and the other output may be exhausted to the atmosphere or some temporary storage medium.
  • the diverter valve 60 is controllable by a control line 62 from controller 50 to provide none, some, or all of the air from air supply blower 36 to the cathode 18 .
  • a control line 62 from controller 50 to provide none, some, or all of the air from air supply blower 36 to the cathode 18 .

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Fuel Cell (AREA)
US12/448,124 2006-12-21 2006-12-21 Method for minimizing membrane electrode degradation in a fuel cell power plant Abandoned US20100068566A1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2006/049025 WO2008088309A1 (fr) 2006-12-21 2006-12-21 Procédé pour réduire au minimum la dégradation d'une électrode à membrane dans une centrale électrique à pile à combustible

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090098427A1 (en) * 2005-11-29 2009-04-16 Reiser Carl A Fuel Cell Power Plant Diverting Air in Response to Low Demand
US20130320910A1 (en) * 2011-02-25 2013-12-05 Carl A. Reiser Controlling pem fuel cell voltage during power transitions and idling
DE102018212130A1 (de) 2018-07-20 2020-01-23 Audi Ag Elektrisches Energiesystem mit Brennstoffzellen

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6096448A (en) * 1997-12-23 2000-08-01 Ballard Power Systems Inc. Method and apparatus for operating an electrochemical fuel cell with periodic fuel starvation at the anode
US6477068B2 (en) * 2000-01-15 2002-11-05 Lucas Industries Limited Apparatus and method for controlling DC power to primary and secondary load utilizing capacitor
US6635370B2 (en) * 2001-06-01 2003-10-21 Utc Fuel Cells, Llc Shut-down procedure for hydrogen-air fuel cell system
US6913845B2 (en) * 2002-10-28 2005-07-05 Utc Fuel Cells, Llc Reducing fuel cell cathode potential during startup and shutdown
US20050196661A1 (en) * 2004-03-04 2005-09-08 Burlatsky Sergei F. Extended catalyzed layer for minimizing cross-over oxygen and consuming peroxide
US7112386B2 (en) * 2002-09-04 2006-09-26 Utc Fuel Cells, Llc Membrane electrode assemblies with hydrogen peroxide decomposition catalyst

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6348768A (ja) * 1986-08-14 1988-03-01 Fuji Electric Co Ltd 燃料電池発電装置

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6096448A (en) * 1997-12-23 2000-08-01 Ballard Power Systems Inc. Method and apparatus for operating an electrochemical fuel cell with periodic fuel starvation at the anode
US6477068B2 (en) * 2000-01-15 2002-11-05 Lucas Industries Limited Apparatus and method for controlling DC power to primary and secondary load utilizing capacitor
US6635370B2 (en) * 2001-06-01 2003-10-21 Utc Fuel Cells, Llc Shut-down procedure for hydrogen-air fuel cell system
US7112386B2 (en) * 2002-09-04 2006-09-26 Utc Fuel Cells, Llc Membrane electrode assemblies with hydrogen peroxide decomposition catalyst
US6913845B2 (en) * 2002-10-28 2005-07-05 Utc Fuel Cells, Llc Reducing fuel cell cathode potential during startup and shutdown
US20050196661A1 (en) * 2004-03-04 2005-09-08 Burlatsky Sergei F. Extended catalyzed layer for minimizing cross-over oxygen and consuming peroxide

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090098427A1 (en) * 2005-11-29 2009-04-16 Reiser Carl A Fuel Cell Power Plant Diverting Air in Response to Low Demand
US20130320910A1 (en) * 2011-02-25 2013-12-05 Carl A. Reiser Controlling pem fuel cell voltage during power transitions and idling
US9130205B2 (en) * 2011-02-25 2015-09-08 Audi Ag Controlling PEM fuel cell voltage during power transitions and idling
DE102018212130A1 (de) 2018-07-20 2020-01-23 Audi Ag Elektrisches Energiesystem mit Brennstoffzellen
DE102018212130B4 (de) 2018-07-20 2024-05-16 Audi Ag Elektrisches Energiesystem und Verfahren zum Betreiben des Energiesystems

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